The fifth wheel coupling of tractor vehicles are pivot-mounted in two bearing blocks that are fastened to the two parallel elements of the frame of the tractor vehicle. The forces exerted by the coupled trailer with vertical and horizontal components are absorbed via the fifth wheel coupling on the bearing blocks, from which they are passed on to the frame elements. The fastening of the bearing block is subjected to a substantial strain in this case.
Vehicle designs are known that have been developed with the goal of a low overall weight, the bearing blocks of the fifth wheel coupling being screwed directly on the frame elements of the vehicle and joined together by cross arms, depending on the application. The screw fastening takes on the transmission of the operating forces of the fifth wheel coupling to the vehicle frame, both in the vertical direction and in that transverse to the direction of travel. For this reason, the screw fastening is correspondingly heavily strained. Therefore, one must use high-quality screws in sufficient numbers.
Beneath the bearing block other structural parts or chassis components are generally mounted, such as the stabilizer arm of the stabilizer mechanism of the rear axle of the tractor vehicle.
EP 1 233 901 B1 describes a coupling assembly for mounting on a tractor vehicle, wherein the bearing blocks have a fastening flange extending in the vertical direction, which is connected to the outside of a vertical section of the respective frame element. This involves a screw connection, in which the screws are arranged horizontally. The vertical force components that are applied act as shear forces on the screws perpendicular to their lengthwise axis, and accordingly the screws must be designed to be stable and of high quality.
Bearing blocks are known from EP 0 694 467 A2 that have a fastening flange extending in the horizontal direction, which is connected to an L-shaped auxiliary frame screwed onto the outside of the vertical section of the frame element. This auxiliary frame is likewise fastened by means of a screw connection to the vertical section of the frame element, and the same shear forces act on this screw connection as in the arrangement of EP 1 233 901 B1.
To avoid shear forces on the screw connection of the fastening flange with the horizontal leg of the L-shaped auxiliary frame, the boreholes through which the screws pass are fashioned with so large a cross section that the screws are overly accommodated in them. This is supposed to ensure that this screw connection only needs to absorb vertical tensile forces and thus is basically subjected to no shear forces. However, these vertical tensile forces are passed on to the screw connection of auxiliary frame and frame element.
In order to prevent the tensile and thrust forces arising during operation of the fifth-wheel coupling from acting as shear forces on the screw connection, thrust plates can be screwed onto the parts of the auxiliary frame in front of and behind the bearing blocks in the direction of travel. These thrust plates lie with bearing surfaces against abutment surfaces of the bearing block in form-fitting manner, in order to absorb the forces transmitted by the latter.
According to another configuration, the parts of the auxiliary frame can fashioned as one piece with the bearing block.